Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Vergĭlĭae, ārum, f. [vergo], the constellation of the seven stars, that rises at the end of spring, the Pleiades, Cic. N. D. poët. 2, 44, 112; Auct. B. Afr. 47; Isid. Orig. 3, 70; cf. Fest. p. 372 Müll.